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Wednesday, June 07, 2017

Dear Dr B: What are the chances of the universe ending out of nowhere due to vacuum decay?

“Dear Sabine,

my names [-------]. I'm an anxiety sufferer of the unknown and have been for 4 years. I've recently came across some articles saying that the universe could just end out of no where either through false vacuum/vacuum bubbles or just ending and I'm just wondering what the chances of this are occurring anytime soon. I know it sounds silly but I'd be dearly greatful for your reply and hopefully look forward to that

Many thanks

[--------]”

Dear Anonymous,

We can’t predict anything.

You see, we make predictions by seeking explanations for available data, and then extrapolating the best explanation into the future. It’s called “abductive reasoning,” or “inference to the best explanation” and it sounds reasonable until you ask why it works. To which the answer is “Nobody knows.”

We know that it works. But we can’t justify inference with inference, hence there’s no telling whether the universe will continue to be predictable. Consequently, there is also no way to exclude that tomorrow the laws of nature will stop and planet Earth will fall apart. But do not despair.

Francis Bacon – widely acclaimed as the first to formulate the scientific method – might have reasoned his way out by noting there are only two possibilities. Either the laws of nature will break down unpredictably or they won’t. If they do, there’s nothing we can do about it. If they don’t, it would be stupid not to use predictions to improve our lives.

It’s better to prepare for a future that you don’t have than to not prepare for a future you do have. And science is based on this reasoning: We don’t know why the universe is comprehensible and why the laws of nature are predictive. But we cannot do anything about unknown unknowns anyway, so we ignore them. And if we do that, we can benefit from our extrapolations.

Just how well scientific predictions work depends on what you try to predict. Physics is the currently most predictive discipline because it deals with the simplest of systems, those whose properties we can measure to high precision and whose behavior we can describe with mathematics. This enables physicists to make quantitatively accurate predictions – if they have sufficient data to extrapolate.

The articles that you read about vacuum decay, however, are unreliable extrapolations of incomplete evidence.

Existing data in particle physics are well-described by a field – the Higgs-field – that fills the universe and gives masses to elementary particles. This works because the value of the Higgs-field is different from zero even in vacuum. We say it has a “non-vanishing vacuum expectation value.” The vacuum expectation value can be calculated from the masses of the known particles.

In the currently most widely used theory for the Higgs and its properties, the vacuum expectation value is non-zero because it has a potential with a local minimum whose value is not at zero.

We do not, however, know that the minimum which the Higgs currently occupies is the only minimum of the potential and – if the potential has another minimum – whether the other minimum would be at a smaller energy. If that was so, then the present state of the vacuum would not be stable, it would merely be “meta-stable” and would eventually decay to the lowest minimum. In this case, we would live today in what is called a “false vacuum.”

If our vacuum decays, the world will end – I don’t know a more appropriate expression. Such a decay, once triggered, releases an enormous amount of energy – and it spreads at the speed of light, tearing apart all matter it comes in contact with, until all vacuum has decayed.

How can we tell whether this is going to happen?

Well, we can try to measure the properties of the Higgs’ potential and then extrapolate it away from the minimum. This works much like Taylor series expansions, and it has the same pitfalls. Indeed, making predictions about the minima of a function based on a polynomial expansion is generally a bad idea.

Just look for example at the Taylor series of the sine function. The full function has an infinite number of minima at exactly the same value but you’d never guess from the first terms in the series expansion. First it has one minimum, then it has two minima of different value, then again it has only one – and the higher the order of the expansion the more minima you get.

The situation for the Higgs’ potential is more complicated because the coefficients are not constant, but the argument is similar. If you extract the best-fit potential from the available data and extrapolate it to other values of the Higgs-field, then you find that our present vacuum is meta-stable.

The figure below shows the situation for the current data (figure from this paper). The horizontal axis is the Higgs mass, the vertical axis the mass of the top-quark. The current best-fit is the upper left red point in the white region labeled “Metastability.”

This meta-stable vacuum has, however, a ridiculously long lifetime of about 10600 times the current age of the universe, take or give a few billion billion billion years. This means that the vacuum will almost certainly not decay until all stars have burnt out.

However, this extrapolation of the potential assumes that there aren’t any unknown particles at energies higher than what we have probed, and no other changes to physics as we know it either. And there is simply no telling whether this assumption is correct.

The analysis of vacuum stability is not merely an extrapolation of the presently known laws into the future – which would be justified – it is also an extrapolation of the presently known laws into an untested energy regime – which is not justified. This stability debate is therefore little more than a mathematical exercise, a funny way to quantify what we already know about the Higgs’ potential.

Besides, from all the ways I can think of humanity going extinct, this one worries me least: It would happen without warning, it would happen quickly, and nobody would be left behind to mourn. I worry much more about events that may cause much suffering, like asteroid impacts, global epidemics, nuclear war – and my worry-list goes on.

Not all worries can be cured by rational thought, but since I double-checked you want facts and not comfort, fact is that current data indicates our vacuum is meta-stable. But its decay is an unreliable prediction based the unfounded assumption that there either are no changes to physics at energies beyond the ones we have tested, or that such changes don’t matter. And even if you buy this, the vacuum almost certainly wouldn’t decay as long as the universe is hospitable for life.

Particle physics is good for many things, but generating potent worries isn’t one of them. The biggest killer in physics is still the 2nd law of thermodynamics. It will get us all, eventually. But keep in mind that the only reason we play the prediction game is to get the best out of the limited time that we have.

this is something I've been wondering about: How would a collapse of the vacuum look?

I assume it would start locally at some random point in the universe and spread from there. How fast does it spread? If it does with the speed of light then we'll not really see it coming. If it is slower, we could actually observe it (and conclude a certain stability from the non-observance).

And what happens if the vacuum collapses? The energy in the Higgs field would be freed and radiated off (I assume). And heavy gauge bosons would suddenly be massless. But I'm not sure if either effect would instantly destroy the earth or if we might have a few moments to marvel at the changed physics.

It's a basic human choice to either follow the evidence where it leads you or to follow mere imagination (whether one's own or someone else's).

We all know that bad consequences (including bad psychological consequences, such as unfounded anxiety) follow from believing in figments of imagination. But appeal to consequences is no counter-argument; logically speaking, doing so begs the question. On the contrary, every legitimate argument -- or legitimate question -- already presupposes logic and evidence as the proper basis of human belief. So the original question more betrays a fundamental philosophic disorientation than a need of scientific education.

The original questioner needs to make up his mind on this basic issue. The "scientific" arguments here may be entertaining but are irrelevant, except perhaps to point out that "no, we have no evidence that the universe will end in that way".

"This meta-stable vacuum has, however, a ridiculously long lifetime of about 10^600 times the current age of the universe, take or give a few billion billion billion years. This means that the vacuum will almost certainly not decay until all stars have burnt out."

Indeed. But even without this knowledge, using only the fact that vacuum decay is independent of humanity, one can guess (in almost all cases correctly) that the chance of this happening within one's lifetime is negligible.

Greg Eagan's sci fi book Schild's Ladder is an amazing story of a "false vacuum" with a lower energy state rushing outward from an experiment gone wrong. It takes place 20KY in the future and is quite minding. He's known for his mathematically oriented fiction. Also see http://kasmana.people.cofc.edu/MATHFICT/mfview.php?callnumber=mf338

Deep cryogenic Bose-Einstein condensates of neutral atom ytterbium (arXiv:1412.5751) and lithium (arXiv:1606.09404) do not precipitate metal, respective boiling points 1500 K and 1600 K. Perhaps the current false vacuum has a protective footnote - or we have the wrong "Higgs" by 5+ GeV short

There's a baked-in assumption within this excellent answer wrt "known unknowns" (like the ones science can explore with more research) and the "unknown unknowns" (for which we cannot access or understand). Even with progress, the more vague can become clear – but that's not issue I raise. The assumption is quite reasonable, as all humans have similar biology and deal with knowledge in a similar way. We have essentially across humankind just one state of "known" as all humans are essentially the only communicating beings in the system, and we all share similar biology and mental processes. It is obvious on deeper inspection that there are other ways of knowing than what humans can access, e.g. just look at the animals that live on the planet: bats and dolphins "know" with different senses, trees and plants collect and use information humans cannot yet measure. It is quite possible that not all beings "know" in the same way, (and, in fact, there is limited evidence of this in people too - that certain models, esp. psychological models are more accessible to some humans than to others). IF (big if here) this is the case, that within a wide distribution of living beings, much wider than what constitutes life on this planet, there are *distinct and separable* mechanisms of "knowing", then the simple bifurcation between "known" and "unknown" states are not only greyed, but they no longer semantically represent a simply a two-state system.

This is a challenge at the heart of our efforts in science, one we have yet to grapple with. Our understanding of separable systems, of the very ideal of separateness itself, may be only a model that is convenient for us to use, but may not represent the actual, underlying reality of the experience in which we exist. I've talked with many other researchers on this, and we have no models reaching into this space yet.

I'm appalled that Dr. Hossenfelder would even bother answering such an inane, paranoid (and likely religiously motivated) question. More rational readers have gotten Bee's backhand over far less silly inquiries, and her tolerance in this case truly surprises me.

I'd like to comment as someone who helps people who are scared the world is about to end. Some of them wake up every day scared that the world is about to end, and the anxiety pervades their entire life. David Morrison who used to field the "ask an astrobiologist" column for NASA says he was told anecdotally via email of several suicides and there was one confirmed suicide by a young school girl in the UK in Bath who thought the world would end in 2012, I haven't had that happen to me but I have had people who say they felt suicidal about the end of the world in the past.

Often it's pseudoscience as for 2012, but recently they've been scared of the false vacuum decay. So this comment is to help and reassure them.

So first, your introduction is a philosophical point, that all our science is based on noticing patterns and order in our world. To give an idea maybe tomorrow someone throws a ball gently in the air and instead of just falling back to the ground in front of them - it continues all the way into outer space and lands in Australia. If we get something that doesn't fit previous patterns at all, like that, we'd have to say our theories are wrong. There is no way really to prove that's impossible.

Nevertheless most people won't worry that if they throw a ball in the air, that it will land in Australia, except perhaps in philosophical discussions. So it's like that here too.

In your conclusion, you try to reassure these people by saying that nobody would know if it did happen - but that's missing the mark. I know you are trying to help, and some people find this reassuring. But others find this one of the most scary future prospects. They worry especially about it as something that could happen to their children, relatives etc.

So, now for the main part of your post, you give the same argument as others that it is very unlikely - but it's hard for most non scientists to understand figures like that. So I've come up with an analogy which helps them to understand.

The chance of winning the Euromillions jackpot is 1 in 139,838,160. The chance of a false vacuum in any particular century according to your calculation is less than the chance of winning a string of seventy three Euromillions jackpots one after another without a single miss. And I don’t mean the chance of anyone winning them all. Rather, it’s as if you bought 73 tickets for Euro Millions, those were the only lottery tickets you ever bought in your lifetime, and you won it every single time. For those of you who live in the States, with a chance of 1 in 292 million of winning the US powerball, then it's as if you play it 70 times, and win every time, as the only lottery you ever play in your life.

Also something that confuses them - for most people when they say there's a "chance" of something happening, they mean it really could happen. E.g. you wouldn't say that a political party has a chance of winning if it is a 1 in 10^600 chance. So in ordinary language, it doesn't really mean "there is a chance of it happening" but rather, that "it can't really happen" like winnning those 70+ lotteries.

I've got a bit more to say but will do it as a separate post because of text limits.

As for the physics we don't know, well a few years ago the Higgs Boson was just a theory and this is one of many ideas about what the universe is like. It's my understanding that this vacuum collapse theory has a fair bit of implausibility written into it because, not only do you have to assume it didn't collapse for the universe to date; you also have to assume that the false vacuum didn't collapse in the very early universe pre-inflation when the entire universe was compressed into a region less than nanometers in size. E.g. by this physics stack exchange calculation that observable universe was 0.88 mm in diameter after inflation - it was about 10^30 times smaller before which would make it 10^-24 nanometers in diameter pre-inflation, or a trillionth of a trillionth of a nanometer in diameter.

Why didn't a universe so dense collapse into a true vacuum already, if it was in a false vacuum state? Professor John Ellis uses this argument to suggest that the discovery means we need new physics (see youtube video). He favours supersymmetry. But there are many such theories and at any rate we know our physics is incomplete and indeed quantum mechanics is not consistent with general relativity, so seems to me the most likely outcome is that some form of new physics will resolve this conundrum. Others have suggested an interaction of the Higgs field with dark matter, for example, or extra Higgs bosons not yet discovered to explain the conundrum.

Though our physics is far advanced over the nineteenth century and early twentieth century physics, still, there may well be discoveries we have yet to make which will make all these speculations seem as archaic to future generations as those speculations about how the Sun could generate its energy from fusion now seem to us.

"The Principle of Sufficient Reason is still as circular as it's always been."

Presumably this is in reply to my earlier remarks.

No, nothing I said was circular. In order for an argument to be circular, it actually has to trace a logical circle, as in I *actually said* that the reason for X is Y, and the reason for Y is X, not *you* presume that I'm doing that. The right way to find out a person's rationale for a given proposition is to *ask them what it is*.

Due to expansion of space, and especially the apparent accelerating expansion, extremely distant regions should be receding at superluminal speeds.

If a false vacuum decayed in those distant regions, then the destruction & its consequences would never reach us -- yes?

Since there's more volume of space in the distant regions of the spherical shells surrounding our patch of universe, and if it's equally likely for vacuum decay to start anywhere, it also seems far more probable for decay to start in those distant regions that can't affect us anymore.

Of course, any intelligent life in those distant regions might reason the same way! This is starting to sound like the "Unexpected Hanging Paradox" ;-)

That life has been evolving for billions of years, should give us confidence that life will persist on our planet for a long time to come. A more immediate concern for humanity are the mass extinction events caused by asteroid impacts, and enormous volcanic eruptions as evidenced by the Siberian Traps, that triggered the Great Dying.

Yes, it was a reply to you. Sorry, I forgot to address you. I didn't say *you* are circular. I am saying that the principle of sufficient reason better be sufficient reason for itself, or else why should it hold.

More seriously, Leibniz got carried away by his belief in the power of human thought. You can't base an explanation for natural phenomena on logic alone. No matter how you turn it, you will always have to postulate something. And the only rationale justification for doing this is that it actually describes what you observe.

"You can't base an explanation for natural phenomena on logic alone. No matter how you turn it, you will always have to postulate something. And the only rationale justification for doing this is that it actually describes what you observe."

Hello Sabine,

It would indeed be ideal if we could always check if a postulate describes what we observe. Unfortunately, it often becomes more complicated.

Because often the postulate itself is untestable, unobservable, unfalsiable, especially at unaccesible scales.Research tends to try and falsify the consequences of the postulate, and that involves human interpretation.

For instance: objekts undergo relativistic lenght contraction.This bybhas itself has not been experimentally confirmed, but we accept this claim because it fits into the context of a theory of which many aspects have been proven.For instance: cosmological redshift is the result of space itself expanding over time. Same comment here.

We could postulate a different origin or physical causal nature for these 2 things, if it is accompanied by an adjusted theory which makes the claims logically acceptable.And there is logic again, weighing on the level of acceptancy of the postulate.

I believe that an improved theory should first bring together all of the strictly unproven aspects of a theory, instead of accepting them 'because it makes sense in the larger context of the theory'. Objectivity recquires it.

From these unproven aspects, accompanied with observed logical inconsistencies, a pattern or a new insight can emerge, as the breeding ground for an improved theory.

-end of postulate- ,)

Best, Koen

P.S. And what is an acceptable amount of research years and money spent, to test a postulate ? And who is to be the judge of that ? Very complicated.

the abductive reasoning method (proposed long ago by Pierce) is the research methodology used in much of theoretical physics, although many quantum gravity researchers have abandoned it (more likely, they never even knew of it) in favor of the hypothetico-deductive method (proposed by Popper and endorsed by Feynman). while you have addressed this in your Nautilus article "What Quantum Gravity Needs Is More Experiments", other so-called 'fundamental' physicists, reveling in their ignorance of the philosophy of science (commonly citing Feynman's' disdainful remark that “Philosophy of science is about as useful to scientists as ornithology is to birds.”) have endorsed the (ridiculous IMO) proposal by Dawid of a 'post-empirical' science that abandons experiment except as an ex post facto tool for verifying their spun-out-of-whole-cloth theories, much to the detriment of the field. It speaks to the usefulness of making the philosophy of science an integral part of the education of physicists (indeed, of all scientists)

My problem with your remarks to me is that you're raising the specter of circularity and Leibniz and rationalism (pure logic being used to divine truths about reality) without addressing anything I actually said, which implies a sort of accusation that my views are tantamount to the ones you're bringing up. (If you don't mean to do this then why are we talking about Leibniz etc.?)

The irony here is that you yourself are being rationalistic instead of empiricist -- an empiricist would ask the subject a question regarding his views as the means of gathering evidence about them, not presume a knowledge of them on the basis of superficial resemblance to some other person's views!

I get why what I'm saying is similar or related, of course, but any suggestion that my views are tantamount to Leibniz etc. are false. Why not just squarely face what I actually said and proceed from there?

I think I owe you another apology :/ My comment above was not addressed at you (in contrast to what I said later), it was addressed at Matthew (who brought up Leibniz - see his comment above). For what your comment is concerned, I think I largely agree. I'd like to add though, as I pointed out, that if one ignores scientific evidence, one has to take into account that one willingly disregards information that might better one's life.

"That life has been evolving for billions of years, should give us confidence that life will persist on our planet for a long time to come."

I don't know if it should or why it should, but it doesn't. If you think so, please re-read my remarks about inference.

I think what was meant is basically Gott's argument: if we are typical observers, we are unlikely to be at the beginning or end of some process. He used this to estimate the future lifetime of various things. There is a huge literature on this, but the basic idea is: go to Egypt, see the pyramids, see some apartment houses built in the 1970s; go back 1000 years later; which do you expect to be there.

On the other hand: an optimist jumps out of the top floor of a skyscraper; as he sails by the second floor, he says "all OK so far".

Hi Sabine, thanks for the post. I think the question is very interesting as to the boundary of science and what I call science-fiction.

True vacuum: The only truth in this is expression that it does not exist in nature. So I see a lot of QFT (like e.g. the 500+ papers about a 750 GeV resonance that seems nonexistent), and it is possible to invent many artificial worlds - just change all "free parameters" of the SM, add a few symmetries or dimensions, etc... So here is my question:

How much is it possible that theories have lost contact with reality? Including within the SM and GR?

sorry that this is off-topic but could you pease let us know when and where you are publishing your commentaries, book reviews, and other articles (e.g. "Science needs reason to be trusted" appears in Nature Physics April 2017 which i just now discovered). many of us find your writing to be the most intelligent and thoughtful writing in the physics 'blog world' ('Not Even Wrong' is the best source for links to other material but offers little insightful analysis while 'Shtetl-Optimized' has seemingly interminably long entries. John Horgan's SA column is also worth reading for the many issues it raises). copyright issues may not allow you to re-publish some of those writings in your blog but referencing them should be okay (and even useful for 'advertising' the journals and magazines where they appear).thanks,

Anyone who is interested in my writing can follow me either on twitter, on facebook, or on G+, where I post (and discuss) links to everything I produce (including this blog). I don't really see the point of dumping links here to pieces (as you guess correctly) I can't reproduce because of copyright reasons. Best,